Secretariat’s dam Somethingroyal is linebred to two obscure stallions, Brown Bud and Caruso, both descending through the same female line. It so happens this female line is also that of the wonderful influence The Tetrarch, so prominent in the pedigree of Nasrullah, grandsire of Secretariat. With The Tetrarch’s sire
Roi Herode also prominent in Secretariat’s dam line, this would seem to provide a plausible explanation of the source of Secretariat’s prowess, particularly given the extreme obscurity of Brown Bud and Caruso.
(Ancestors depicted in red are from the same female line). Amazingly, Brown Bud himself is also linebred to that same female line, as can be seen in the abbreviated pedigrees below:
So the dam line of Secretariat is line bred again and again through the most obscure ancestors, to the dam line of one of the main influences in the pedigree of his grandsire, Nasrullah.